Quince, meaning “fifteen” in Spanish, forms the beginning of quinceañera.
The word directly points to the celebration’s traditional age. Quince is a cardinal number, meaning the quantity fifteen. It is not the same as quinto, which generally means fifth, or cinco, which means five. Quinceavo is associated with a fifteenth part or ordinal-style usage in some contexts, not the basic number used in the celebration’s name.
The rest of quinceañera identifies a feminine person associated with that age. In everyday English, the full word can refer to either the young woman or her birthday celebration, depending on context.
Because the celebration has spread across countries and languages, English spellings sometimes omit the tilde in quinceañera. The Spanish spelling preserves the ñ and makes the word’s pronunciation and identity clearer.